Sclerotherapy treats veins that are twisted and enlarged, known as varicose veins. Varicose veins are usually in the legs. Sclerotherapy also treats spider veins, a mild form of varicose veins. Sclerotherapy usually works best on small varicose veins.

Sclerotherapy involves using a needle to put a solution into the vein. The sclerotherapy solution causes the vein to scar. The scarring forces blood through healthier veins. The collapsed vein then fades.

After sclerotherapy, treated veins tend to fade within a few weeks, although they might not disappear completely. It can take a month or more for full results. Some veins need more than one sclerotherapy treatment.

Sclerotherapy generally has few serious complications.

Side effects that can occur where the needle goes into the skin include:

• Bruising.
• Raised red areas, called hives.
• Small skin sores.
• Darkened skin.
• A number of tiny red blood vessels.

These side effects usually go away within days to weeks. Some side effects may take months or longer to go away completely.

Less-common side effects of sclerotherapy that might need treatment include:

• Inflammation. This is usually mild but may cause swelling, warmth and discomfort around the site where the needle went into the skin. Taking a pain reliever you can get without a prescription might help. These include aspirin and ibuprofen (Advil, Motrin IB, others).

• Blood clot. If a lump of clotted blood forms in a treated vein, it might need to be drained. Rarely, a blood clot can travel to a deeper vein in the leg, a condition known as deep vein thrombosis.

  Deep vein thrombosis carries a risk of a blood clot traveling from the leg to the lungs and blocking a vital artery. This is known as a pulmonary embolism. It's a very rare complication of sclerotherapy that needs immediate medical care. The symptoms include trouble breathing, chest pain or dizziness, or coughing up blood.

• Air bubbles. Tiny air bubbles can rise in the blood. This might not cause symptoms. But symptoms might include seeing light flashes, having headaches, fainting and having nausea.

  These symptoms usually go away. But call your health care provider for problems with moving or feelings in arms or legs after the procedure.

• Allergic reaction. An allergic reaction to the solution used for treatment is possible, but uncommon.

Before the procedure, a health care provider does a physical exam. The provider examines your veins and checks for blood vessel disease.

The provider asks questions about your medical history. Information needed about your medical history includes:

• Recent illnesses or medical conditions, such as a heart condition or a history of blood clots.
• Allergies.
• Other treatments you've had for varicose veins and the results.
• Medicines or supplements you take, especially aspirin, ibuprofen (Advil, Motrin IB, others), naproxen sodium (Aleve, Anaprox DS), blood thinners, iron supplements or herbal supplements.

Aspirin, ibuprofen, naproxen sodium or blood thinners can increase the risk of bleeding. If you take one or more of these, a member of your health care team can tell you how and when to stop taking them before the procedure.

Before sclerotherapy, a health care provider might ask for an ultrasound test of the legs. This is likely if the veins are causing symptoms. Ultrasound is a painless procedure that uses sound waves to create pictures of structures inside the body.

Sclerotherapy is typically done in a health care provider's office. It generally takes an hour or less to complete.

Before the procedure

Don't shave your legs or use lotion on them. Wear loose, comfortable clothing.

During the procedure

You lie on your back with your legs slightly raised. A member of your health care team cleans the area to be treated. Then your care provider uses a small needle to slowly put solution into the vein.

The solution, usually a liquid, works by irritating the lining of the vein, causing it to swell shut and block the flow of blood.

Some people feel minor stinging or cramping when the needle goes into the vein. Tell your provider if it hurts a lot. Pain might result from the solution leaking from the vein into the tissue around it.

After removing the needle, your provider applies pressure to the area and massages it to keep blood out of the vein and to spread the solution. The provider might tape a pad onto the injection site to keep pressure on the area before moving on to the next vein.

The number of shots depends on the number of veins being treated.

After the procedure

You can get up and walk around soon after the procedure. Walking and moving helps keep blood clots from forming.

Wearing compression stockings or bandages — usually for about two weeks — will keep pressure on the treated veins. Don't shave your leg or use lotion on it until the site heals.

Most people return to their regular activities on the same day, but you might want to have someone drive you home after the procedure. Your health care provider might tell you to avoid hard exercise for two weeks after the procedure.

Avoid having the treated areas in sun for two weeks, as well. Or use sunscreen with at least 30 SPF. Being in the sun can lead to dark spots on the skin, especially for those with dark skin.

Results of sclerotherapy for small varicose veins or spider veins usually show in 3 to 6 weeks. Larger veins might take 3 to 4 months. However, you might need more than one treatment to get the results you want.

Veins that respond to treatment generally don't come back. But new veins can appear.

Your health care provider might ask you to return for a follow-up visit about a month after the procedure to see the results. You might need more sessions. Generally, you need to wait about six weeks before having another sclerotherapy session.